The present invention relates to a curable organopolysiloxane composition or, more particularly, to a curable organopolysiloxane composition with excellent workability and curing behavior imparted by the addition of a moderator for the crosslinking reaction.
As is well known, the crosslinking reaction in a class of curable organopolysiloxane compositions proceeds by the mechanism of the so-called hydrosilation in which an addition reaction takes place between aliphatically unsaturated groups or, typically, vinyl groups bonded to the silicon atoms of an organopolysiloxane and hydrogen atoms directly bonded to the silicon atoms in an organohydrogenpolysiloxane in the presence of a noble metal, e.g. platinum, catalyst and such curable organopolysiloxane compositions of so-called addition-type are widely used in various applications in which curing of the composition should desirably be effected at room temperature or at a relatively low temperature, if heating is required.
A problem or disadvantage involved in the addition-type curable organopolysiloxane composition is that the pot life of a ready-mixed composition is sometimes unduly limited with poor workability in the practical application of the composition and, when extension of the pot life is intended by the addition of a reaction moderator, difficulties are encountered in obtaining good balance between the pot life and curing behavior of the composition although various kinds of compounds have been proposed as the moderator including perchloroethylene (see Japanese Patent Publication No. 47-6111), acetylenic alcohols (see Japanese Patent Publication No. 44-31476), acrylonitrile (see Japanese Patent Publication No. 45-22018), maleate compounds (see Japanese Patent Publication No. 56-4655), silylated compounds (see Japanese Patent Publication No. 59-133252) and others.
These compounds proposed in the prior art as a moderator of the addition reaction, however, have their respective disadvantages. For example, perchloroethylene is effective only when it is used in a large amount so that no clear demarcation can be found between the effect by dilution with a solvent and the effect of reaction retardation per se by the compound. Such a composition admixed with a large volume of perchloroethylene can no longer be used as a solventless coating composition as a matter of course. The acetylenic unsaturation in the acetylenic alcohol has reactivity with the silicon-bonded hydrogen atoms in the organohydrogenpolysiloxane so that a curable organopolysiloxane composition admixed with an acetylenic alcohol is subject to decrease in the curability during storage due to the consumption of the silicon-bonded hydrogen atoms as the functional groups pertaining to the curing reaction. Acrylonitrile also has a relatively low activity for the retardation of the crosslinking reaction so that no desired effect can be obtained by the addition of a small amount thereof while increase of the amount may cause incomplete curing of the composition in addition to the problem in the workers' health and environmental pollution due to the unpleasant odor and toxicity of the compound. The maleate compounds have similar problems to acrylonitrile. The silylated compounds are also poorly effective and the desired effect of reaction retardation can be obtained only by the addition of a relatively large amount thereof. In addition, silylated compounds are generally susceptible to hydrolysis and must be handled or stored with particular care.